A well-known type of pressure reducing valve embodies a housing having an inlet opening for a high pressure gas and a discharge opening for the gas at reduced pressure. Flow through the housing is controlled by a main valve that is moved away from its seat against the force of a spring by pressure from the inlet side of the valve applied to a piston that can lift the valve member away from its seat against the action of the spring. The application of pressure to the piston is controlled by a pilot valve which controls the flow of high pressure gas to the actuating piston for the main valve. The pilot valve is responsive to pressure on the outlet side of the main valve, the pilot valve being controlled by a spring which tends to move the pilot valve toward open position and a pressure responsive member acting in opposition to the spring and arranged so that an increase in the discharge pressure of the valve will cause the pilot valve to move toward its seat, thus reducing the pressure applied to the piston that controls the main valve and permitting the main valve spring to move the main valve toward its seat, thereby reducing the discharge pressure.
Valves of this general type are in wide use. Currently available valves are subject to the objections that they are bulky; that replacement of worn components such as the pilot valve and main valve and their respective seats is difficult and expensive; and that they are noisy in operation due to the high velocity and sometimes improperly controlled flow of fluid through them.
It has been proposed to ameliorate the noise problem by employing a valve member with grooves in the surface thereof over which the gas flows as it passes through the orifice provided by the main valve member and the valve seat. A valve of this kind is shown in the Muller U.S. Pat. No. 3,791,413. In valves of this construction, the effect of the grooves in the valve member varies with the position or degree of opening of the valve member.
Prior devices of this general type also have been bulky. Also, replacement of the parts subject to wear, such as the pilot valve assembly and the main valve seat and valve member, have been expensive and time-consuming operations.